This invention relates to a needle receiving and transferring apparatus for a sewing machine and more particularly to a device which is capable of alternately using a single needle as both, upper and lower needles.
Conventionally, a hand stitch machine has been constructed so that a pair of needle bars 1 are mounted opposite to each other with a needle plate (not shown) therebetween, as shown in FIG. 4. A needle 2 with pointed extremities at the opposite ends thereof, as shown in FIG. 5, is transferred from the upper needle bar 1 to the lower needle bar 1 and vice versa in response to up and down movement of the needle bars 1.
The needle 2 is provided with a needle eye 3 at the center thereof and arcuated recesses 4 on the opposite sides thereof adjacent to its upper and lower pointed extremities. The needle 2 is held stationary by urging or pressing balls 5 against the recesses 4, as shown in FIG. 6.
Each of the balls 5 is held in a race or groove 1a formed on the inner periphery of the needle bar 1 and also held in an opening 6a in a ball holder 6 inserted in a cylinder 7. When the bottom portion 8 of the needle bar 1, beneath the race or groove 1a, is in contact with the balls 5, the balls are urged toward the central axis of the needle bar 1 and fitted in the recesses 4, thereby clamping the balls therein.
The needle 2 is downwardly moved by a needle bar elevating mechanism (not shown) from a position where its upper pointed extremity is held in the upper needle bar 1, as shown in FIG. 6, to a position where it assumes its bottom dead center. At this time, a collar 9, fixed to the cylinder 7, impinges against the top of a needle bar bearing 10, secured to the machine frame to prevent it from moving downwardly. The needle bar 1, however, is further lowered against a spring 30 by the needle bar elevating mechanism. At the beginning of downward movement of the needle bar 1, the needle bar 1 is followed by the ball holder 6 to lower the latter under the influence of a spring 31. Then, the ball holder 6 stops in a position where the balls 5 abut against the lower ends of slots 7a in the housing 7. Thereafter, solely the needle bar 1 is further lowered. As a result, the bottom portion 8 of the needle bar 1 is moved downwardly away from the balls 5 to release the force by which the balls 5 were urged against the recesses 4 in the needle 2.
In this condition, the needle 2 is allowed to insert its lower pointed extremity into the lower needle bar 1 which engages and holds the balls 5 in the recesses 4 in the needle 2, completing a receiving and transferring operation of the needle 2.
With the same arrangement as aforementioned, when the lower needle bar 1 assumes its top dead center position, the balls 5 are disengaged from the recesses 4 in the needle 2, thus releasing the lower pointed extremity of the needle 2. At the same time, the upper pointed extremity of the needle 2 is held in the upper needle bar 1. In this manner, the needle 2 is received and transferred to continue a sewing operation as performed by a sewing machine.
FIGS. 7A-7F show successive steps of the sewing operation. More specifically, FIG. 7A is a representation of the manner in which an upper looper 12 is inserted into a loop of a thread 11. FIG. 7B is a view of the manner in which the thread 29 loop is retained or entangled by the upper looper 12. FIGS. 7C-7E are representations of the manner in which the needle 2 is lowered for the sewing operation. FIG. 7F is a view of the manner in which the thread loop is retained or entangled by a lower looper 13.
Such a conventional needle receiving and transferring apparatus for a hand stitch machine is disadvantageous in that high impact noises are repeatedly produced whenever the needle 2 is transferred between the upper and lower needle bars 1, since this is accompanied by collision of the collar 9 with the bearing 10. A further disadvantage is that the springs 30, 31 mounted in the needle bar 1 are required to become repeatedly compressed because of the repetitious relative motion of the ball holder 6 and the housing 7 in the needle bar, thereby shortening the operating life of the apparatus.
Further, difficulty is involved in setting the pressure intensity of the springs 30 or 31. For instance, if the spring 30 is too soft, the impulsive force caused by the collision of the collar 9 with the bearing 10, makes the cylinder 7 deviate from a position where the needle is located when the needle is received and transferred.
In contrast, if the spring is too stiff, problems in mechanical strength arise. Namely, a spindle 32 secured to the cylinder 7 is readily broken since the needle bar as a whole is slender. On the other hand, if the other spring 31 is too soft, this would permit the ball holder 6 to creep into the spring against the bias of the spring when the needle is transferred. In such a case, the recesses 4 in the needle 2 would come out of alignment with the balls 5, and result in a failure in chucking.